I've heard people installing a larger master cyl. Also start with clean fluid, also bleed the ABS system. Sometimes dirt or old fluid will reduce effective braking. the e30's braking system is pretty balanced to begin with. Obviously more braking required to the front due to the weight of the engine etc. The only solution I have heard about improving stopping distance is bigger brakes. more surface area faster stopping but as mentioned who is to stay with any of these mods you just won't end up locking up and skidding?